Method and apparatus to determine golf ball trajectory and flight

ABSTRACT

A launch monitor system including a support structure, a first light-reflecting element disposed on this support structure, a lighting unit and an camera unit. A computer receives signals generated by light patterns received by the camera unit and computes a variety of flight characteristics for the object. The system may be moved back and forth to vary the field-of-view of the camera unit. The system also computes and displays object trajectories from the computed flight characteristics which account for the characteristics of the object and the atmospheric conditions.

This application is a divisional application of U.S. application Ser.No. 09/156,611 filed on Sep. 18, 1998, now U.S. Pat. No. 6,241,622,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Apparatus for measuring golf ball flight characteristics are known (U.S.Pat. Nos. 4,063,259; 4,375,887; 4,158,853; and 4,136,387). Techniques ofdetecting golf club head position and golf ball position shortly afterimpact using photoelectric means to trigger a flash to permit aphotograph to be taken of the club head have been disclosed (U.S. Pat.Nos. 4,063,259 and 4,375,887). Golf ball or golf club head movement hasbeen determined by placing reflective areas on a golf ball along withuse of electro-optical sensors (U.S. Pat. No. 4,136,387). Theelectro-optical sensing of light sources on both the golfer's body andclub has also been disclosed (U.S. Pat. No. 4,137,566). In addition,apparatus for monitoring a golfer and the golf club being swung has alsobeen disclosed (U.S. Pat. No. 4,137,566).

One particularly troublesome aspect of past systems for measuring golfball flight characteristics relates to their lack of portability. Inthis regard, prior systems have generally required cameras, sensors andstrobe lights set up in various positions about the golfer. In addition,past systems have not had the ability to be utilized outdoors but havehad to be set up indoors under less than ideal or realistic golfingconditions. As prior golf ball and/or golf club monitoring systems havenot been portable and have not been capable of practical use outdoors,the systems have not been usable in the most desirable teaching or clubfitting locations, e.g., on an outdoor driving range. Also, while thesystems disclosed in the related applications and patents mentionedabove, which are incorporated herein by reference) are portable and arecapable of use outdoors, further improvements related to increasedportability would be desirable to allow easier transportation of theunit between sites and easier movement of the unit at any particularsite.

One additional area that has not been adequately addressed by past golfball launch monitoring systems relates to the area of predicting flightpath differences based on different physical characteristics of golfballs and/or different atmospheric conditions that a golfer mayencounter after being tested by the launch monitor system. It wouldtherefore be desirable to provide a system which measures the launch orflight characteristics of a golf ball having a particular construction,such as a two-piece construction and under ideal atmospheric conditionsand then provide the golfer with revised golf ball flight results basedon computer predictions for golf balls having different physicalcharacteristics (such as a three-piece golf ball) and differentatmospheric conditions (such as higher elevations, higher humidity ormore adverse wind conditions).

SUMMARY OF THE INVENTION

Broadly, the present invention comprises method and apparatus formeasuring the speed, direction, and orientation of a golf ball and fromsuch data computing the flight path of the golf ball.

It is a feature that the method and apparatus particularly apply to golfequipment and that the present invention provides a golfer with datarelating to the variables of his swing useful in improving the swing andin selecting advantageous equipment for use, including the types of golfballs.

In particular, the present invention contemplates a launch monitorsystem for measuring launch characteristics of a golf ball from datataken when the golf ball is in a predetermined field-of-view. The systempreferably includes a support structure, which is a single, portablesupport structure, light-reflecting elements disposed on the supportstructure, a lighting unit, and camera units. The lighting unit includesa light source directed at the light-reflecting elements for reflectinglight into the predetermined field-of-view, and the electro-opticalunits, disposed on the support structure in proximity to thelight-reflecting elements, are directed toward the predeterminedfield-of-view. The light-reflecting elements include an aperture and thecamera units are disposed to monitor the predetermined field-of-viewthrough the aperture.

This allows, for example, the system to be used outdoors in a grassyarea and for the hitting area to be slightly varied to move the playeraway from divots, etc. The support elements may include slide pads,wheels, or combinations of both. The support elements may beheight-adjustable to vary the orientation and direction of view of thesystem and, specifically, the camera units. As an additional aspect ofthe invention, a distance calibrator is provided for calibrating thedistance between the camera unit or units and the predeterminedfield-of-view.

It is an object of the system to measure launch characteristics of anobject after it is struck by a striking instrument.

It is a further object of the invention to provide computing means tocalculate the trajectory of the object from the launch characteristicsand information on the environmental conditions and the object'scharacteristics and to generate statistics on these object trajectories.

It is a further object of the invention to provide a control means tomanage the tasks performed by the system including camera activation,shutter control, image capture, calculation of launch characteristics,calculation of object trajectories, and generation of object trajectorystatistics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the presentinvention;

FIG. 2 is a top view thereof;

FIG. 3 is a side elevational view of the system shown in FIGS. 1 and 2;

FIG. 4 is an elevational view of the light receiving and sensory gridpanel located in each camera;

FIG. 5 is a perspective view of a three-dimensional rectilinear fieldshowing a golf ball at two different positions I and II;

FIG. 6 is a perspective view of a second embodiment of this invention;

FIG. 7 is a top view of the apparatus shown in FIG. 6 and generallyshowing calibration of the system;

FIG. 8 is a side elevational view of the system shown in FIGS. 6 and 7;

FIG. 9 is a top view of the system shown in FIGS. 6-8 and generallyshowing a golf ball in place under operating conditions;

FIG. 10 is a partial, cut-away top view of the system shown in FIGS. 6-9illustrating the strobe lighting unit;

FIGS. 11A and 11B is a diagram of a voltage amplifier and regulatorcircuit and a trigger and discharge circuit, respectively, used in thesystem shown in FIGS. 6-10;

FIG. 12 is an example of a Fresnel lens used in the present invention;

FIG. 13 illustrates a light pattern without a Fresnel lens;

FIG. 14 illustrates a light pattern with a Fresnel lens;

FIG. 15 is a perspective view of the calibration fixture carryingfifteen illuminable areas;

FIG. 16 is a perspective view of an unassembled rod useful for allowingmovement of a system constructed in accordance with the invention;

FIG. 17 is an elevational view of the rod of FIG. 16 shown in anassembled condition;

FIG. 18 is a flow chart describing the operation of the system;

FIG. 19 is a flow chart describing the calibration of the system;

FIG. 20 is a flow chart describing the determination of dots in theimage;

FIG. 21 is a graph showing the trajectory of the golf ball as calculatedby the system; and

FIG. 22 is an example of a contour map of the total distance a golf balltravels under specified conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a preferred first embodiment of the invention in theform of a portable launch monitoring system 10 including a base orsupport structure 12 and attached support elements 14, 16. Supportelements 14, 16 are specifically shown as slide pads each includingV-shaped notches 18, 20, which allow the pads 14, 16 to slide along arod 22. Another slide pad 24 attached to the system 10 at the rear(shown in FIG. 3) similarly slides along a rod 26. One or more slidepads 14, 16, and 24 may be replaced by other support elements withdifferent configurations or methods of moving, such as wheels. By theterm “slide pads,” applicants intend to cover any elements allowing thesystem 10 to slide or move back and forth relative to a predeterminedfield-of-view. Slide pads 14, 16 include a height adjustment featureallowing the front comers of system 10 to be raised or lowered forleveling purposes. Specifically, each slide pad 14, 16 is attached tosupport structure 12 by respective threaded rods 28, 30 and nuts 32, 34fixed to the support structure 12. Rods 28, 30 each include a driveportion 28 a, 30 a that may be used to adjust pads 14, 16.

Referring now to FIGS. 1-3, launch monitoring system 10 further includesfirst and second camera units 36, 38, a centrally disposed control box40, and a dual strobe lighting unit 42. First and second camera units36, 38 are preferably ELECTRIM EDC-1000U Computer Cameras from ElectrimCorporation in Princeton, N.J. Charge coupled device or CCD cameras arepreferred but TV-type video cameras are also useful. The angle betweenthe two cameras' line of sight is preferably in the range of 10-30, with22 being most preferable. Each of the cameras 36, 38 has alight-receiving aperture, shutter, and light sensitive silicon panel 39(see FIG. 4, showing a silicon panel, which also generally correspondsto an image captured by the cameras and used by the system). The camerasare directed and focused on a predetermined field-of-view in which agolf ball moves and is imaged.

As shown in a three-dimensional, predetermined, rectilinearfield-of-view (shown in phantom) in FIG. 5, golf ball 41 preferably hassix (6) reflective, spaced-apart round areas or dots 41 a-f placedthereon. Golf ball 41 is shown in two positions I and II to illustratethe preferred embodiment, corresponding to the locations of the golfball 41 when imaged by the system. In positions I and II the golf ballis shown after being struck. The image taken at position I occurs at afirst time and occurs at in position II at a second time. The preferreddiameters of the round dots 41 a-f range from one-tenth ({fraction(1/10)}) to one-eighth (⅛) of an inch, but other sized and shaped areascan be used. Dots 41 a-f are preferably made of reflective materialwhich is adhered to the golf ball. The Scotchlite™ brand beaded materialmade by Minnesota Mining and Manufacturing (3M) is preferred for formingthe dots. Comer-reflective retro-reflectors may also be used.Alternatively, painted spots can be used that define contrasting areas.The number of dots or areas may be as few as three (3) and up to six (6)or more for the golf ball, provided each dot or area reflects light fromthe golf ball in both positions shown in FIG. 5. As a result of thepositioning of the cameras 36, 38 and the dots 41 a-f,both cameras 36and 38 are capable of receiving light reflected by dots 41 a-f, whichappear as bright areas 39 a-f on the silicon panel 39 (as shown in FIG.4) and the corresponding image. Alternatively, the dots may benon-reflective, appearing as dark areas 39 a-f on the silicon panel.

Reflective materials as compared with the coated surface of the golfball can be as high as nine hundred (900) times brighter where thedivergence angle between the beam of light striking the dots 41 a-f andthe beam of light from such dots to the camera aperture is zero or closeto zero. As the divergence angle increases, the ratio of brightness ofsuch dots 41 a-f to the background decreases. It will be appreciatedthat electromagnetic waves outside the range of visible light, such asinfra red light, may be used to make the flash light invisible to thegolfer.

The control box 40 communicates via an asynchronous protocol via acomputer's parallel port to the camera units 36, 38 to control theiractivation and the dual strobe lighting unit 42 to set off thesuccessive flashes. Dual strobe lighting unit 42 includes two VivitarAutomatic Electronic Flash Model 283 strobe lights mounted on top of oneanother. These strobe lights sequentially direct light onto a beamsplitter 43 and then out of the unit through windows 44 and 46 toreflective elements or panels 48, 50 and then to the predeterminedfield-of-view. Panels 48, 50 may be plates formed of polished metal,such as stainless steel or chrome-plated metal. Other light reflectiveelements may also be used without departing from the spirit or scope ofthe invention. Each reflective panel 48, 50 includes an aperture 52, 54.Cameras 36, 38 are fixed on support structure 56, 58 and are therebydisposed with their respective lenses 60, 62 directed to thepredetermined field-of-view through apertures 52, 54. Video lines 64, 66feed the video signals into control box 40 for subsequent use.

The locations of the strobe lights, beam splitter, reflective elementsand cameras allow the light directed from the strobe to enter thefield-of-view and be reflected back from the ball, due to the reflectivedots, to the camera lenses through the apertures. In another embodiment,ring-shaped strobe lights can be used which surround each camera lens.Since the ring-shaped strobe lights are positioned close to the lensesand the center axis of the strobe is aligned with the center of thelenses, the light once reflected off the markers would enter the lenses.Thus, eliminating the need for the reflective elements.

Preferably, telescoping distance calibrators 68, 70 are affixed tosupport structure 12. The telescoping members are used in calibratinglaunch monitoring system 10 at the appropriate distance from an objectto be monitored. Distance calibrators 68, 70 are extendable members forexample conventional radio antennae can be used. Calibrators 68, 70 areused in conjunction with a calibration fixture shown in FIG. 15 anddiscussed in detail below with respect to the second embodiment. It willbe understood that the same calibration fixture is preferably used withboth the first and second embodiments. At least one distance calibratorshould be used.

In this first embodiment, a microphone 72 is used to begin the operationof the system 10. When the golf club hits the golf ball, a first imageof the golf ball 41 in the predetermined field-of-view is taken, asshown in FIG. 5 position I, in response to the sound being transmittedby the microphone 72 to the system 10. Since the system 10 is preferablyused to monitor only the golf ball, although it could also be used tomonitor the golf club, the first of the two images needs only to betaken once the golf ball is struck by the club, as illustrated by thegolf ball in position I of FIG. 5. A laser or other apparatus (notshown) can also be used to initiate the system. For example, theinitiating means can include a light beam and a sensor. When the movinggolf ball passes through the light beam the sensor sends a signal to thesystem. When the laser is used, the laser is arranged such that a golfclub breaks the laser beam just after (or at the time) of contact withthe golf ball. That is, the laser is aligned directly in front of theteed golf ball and the first image taken as or shortly after the golfball leaves the tee. The operation of the first embodiment is discussedin detail below after a description of the second embodiment.

FIGS. 6-10 illustrate a second embodiment of the present invention thatfurther reduces the size and therefore increases the portability of thesystem.

Launch monitoring system 100 includes a base or support structure 112that may also have a cover 113. Slide members or pads 114, 116 areutilized at a lower front portion of support structure 112 and includenotches 118, 120 for receiving a rod 190 along which pads 114, 116 mayslide. As shown in FIGS. 7 and 8, wheels 122, 124 replace the pad 24disclosed with respect to the first embodiment shown in FIGS. 1-3.Wheels 122, 124 are attached for rotation and to support structure thatincludes a handle 126 for allowing an operator to move launch monitoringsystem 100 back and forth along the ground. Like the first embodiment,this second embodiment also includes threaded rods 128, 130 andrespective nuts 132, 134 for allowing height adjustment at the front oflaunch monitoring system 100. The wheels may also be height adjustedrelative to the support 112 to allow the system 100 to be adjusteddepending on the terrain on which the system is placed. Although notshown for the second embodiment, the systems in the first and secondembodiments also have a computer and monitor 43 (as shown in FIG. 1).The computer and monitor may be combined into a single element or beseparate elements. The computer has several algorithms and programs usedby the system to make the determinations discussed below.

As further shown in FIGS. 6 and 7, first and second camera units 136,138 are affixed to support structure 112. These electro-optical units136, 138 are smaller than those disclosed with respect to the firstembodiment and are preferably the ELECTRIM EDC-1000HR Computer Camerasavailable from the Electrim Corporation in Princeton, N.J. The camerasalso have light-sensitive silicon panels as in the first embodiment. Thecameras 136, 138 each have a line-of-sight, which are illustrated assolid lines in FIG. 9, that are directed to and focused on thepredetermined field-of-view. As illustrated in FIG. 9 with the brokenlines, the cameras' fields-of-view are larger than are necessary toimage just a single golf ball. Thus, the predetermined field-of-view isthe cameras' fields-of-view at the location where the cameras'lines-of-sight intersect.

A control box 140 is provided and includes a strobe light unit at afront portion thereof. As shown in FIG. 10, strobe light unit iscomprised of a single flash bulb assembly 144, the related circuitry,and a cylindrical flash tube. The operation of which are described inmore detail below. As best shown in FIG. 6, the reflective elements orpanels 146, 148 are mounted to support structure 112 in a similarorientation to those discussed above with respect to the firstembodiment. Reflective panels 146, 148 also include respective apertures150, 152. Referring to FIGS. 6 and 7, cameras 136, 138 are mounted suchthat the lenses 137, 139 are directed through the respective apertures150, 152 in the reflective panels 146, 148 to the predeterminedfield-of-view. Video lines 154, 156 from the respective electro-opticalunits 136, 138 lead to control box 140. Like the first embodiment, thisembodiment includes distance calibrators also in the form of antenna158, 160, and microphone 162 that also is used to initiate the operationof the system. Again, a laser or other method of initiating the systemcould be used.

Referring to FIG. 10, the increase in the portability of the secondsystem 100 over the first system 10 is also due to the use of a singleflash bulb assembly 144, and associated circuitry in the strobe lightunit. The strobe light unit has a single flash bulb assembly 144 capableof flashing faster than every 1000 microseconds. The circuits used withthe strobe light unit are the subject of another commonly assignedapplication (application Ser. No. 09/008,588), which is incorporatedherein in its entirety by express reference thereto. A diagram of thecircuit used for the strobe light unit is illustrated in FIGS. 11A and11B. As there is only a single flash bulb in the strobe light unit, itwill be appreciated that two additional reflective elements arerequired. Referring to FIG. 6, a third light-reflecting panel 164reflects about one-half of the light from flash bulb into panel 146while a fourth light-reflecting panel 166 reflects the other half of thelight into light-reflecting panel 148. The respective set-ups for boththe calibration mode and the operation mode of system 100 are shown inFIGS. 7-8 and 9, respectively.

To increase the amount of light directed to the reflective elements orpanels 146, 148, 164, and 166, the system 100 preferably has an opticalor Fresnel lens 168 (as shown in FIG. 12) inserted at the front of thecontrol box 140, placed between the flash bulb assembly 144 and thethird and fourth reflective elements or panels 164, 166 as shown inFIGS. 6 and 10. A lens assembly is formed by the lighting unit and theFresnel lens. The Fresnel lens 168 directs light from the flash bulbassembly 144 to the third and fourth reflective elements 164, 168. TheFresnel lens has a collimating effect on the light from a cylindricalflash tube. Thus, light pattern with the Fresnel lens 168 controls thedispersion of light as shown in FIG. 14. FIG. 13 shows the light patternwithout the Fresnel lens 168. The lens 168 preferably has a focal lengthof about 3 inches, and the center of the flash bulb assembly 144 is lessthan 3 inches behind the lens. This arrangement allows the system 100 tohave a smaller flash bulb assembly 144 than without the lens 168 becausethe collimation of the light increases the flux of light at the golfball in the predetermined field-of-view. This increase in the fluxallows the possibility of using other reflective materials (or none atall), as well as the use of the system in brighter lighting conditions,including full-sun daylight.

As shown in FIG. 15, and in use with the system in FIGS. 7 and 8, acalibration fixture 170 is provided to calibrate the system. Althoughthis discussion is with reference to system 100, it applies equally tosystem 10. The fixture 170 includes receiving elements or tabs 172, 174extending outwardly from outer legs 176, 178 for receiving an endportion of the distance calibrators 158, 160. When positioned at thislocation in accordance with the distance calibrators 158, 160, a centralleg 180 of fixture 170 is disposed at the proper location for a golfball 182 used in a launch monitoring operation, as shown in FIG. 9. Golfball 182 also has the pattern of retro-reflective dots as golf ball 41(as shown in FIG. 5) in the first embodiment. Calibration fixture 170further includes an optical level indicator 184 on a top surface thereoffor allowing fixture 170 to be leveled before the calibration procedure.Finally, spikes 186, 188 (as shown in FIG. 8) extending from the bottomof fixture 170 are inserted into the turf to stabilize fixture 170during the calibration procedure. It will be appreciated thatcalibration fixture 170 and golf ball 182 are also preferably used withthe first embodiment shown in FIGS. 1-3 in the same manner discussedhere. In this regard, fixture 170 has a pattern of retro-reflective dots170 a-o, as shown in FIG. 15. Applicants have found that only 15 dots(as opposed to the twenty dots used on the calibration fixture of theparent application-application Ser. No. 08/751,447) are necessary. Sincethe longitudinal movement of the golf ball is greater than its verticalmovement during the time between the two images (see, e.g., FIG. 4), thecalibration of the system need not be as precise in the verticaldirection. Therefore, fewer dots in the vertical direction on thecalibration fixture are needed to adequately calibrate the system.

As a further means for providing portability to the launch monitoringsystems of the present invention, and as shown in FIGS. 16 and 17, rod190 (which may also be the same as rod 22 for system 10) may be easilydisassembled for transport and reassembled on site before operation ofany of the disclosed launch monitoring systems. Specifically, rod 190may comprise a plurality of sections 190 a-d. Preferably, each of thesesections comprises a hollow tube containing a single elastic cord 192affixed at opposite ends of rod 190. Cord 192 has a relaxed length lessthan the total length of rod 190 in order to hold sections 190 a-dtogether. Sections 190 a, 190 b, 190 c have respective reduced diameterportions 194, 196, 198 that fit within respective ends of sections 190b, 190 c, 190 d. Pins 200, 202 are provided at opposite ends of rod 190to allow the rod 190 to be secured into the turf.

The use of both systems 10 and 100 is shown generally in FIG. 18.

At step S101, the system starts and determines if this is the first timethe system has been used. By default, the system will use the lastcalibration when it is first activated. Therefore, the system must becalibrated each time the system is moved and/or turned on.

At step S102, the system is calibrated to define the coordinate systemto be used by the system.

After the system is calibrated, the system is set at step S103 foreither the left- or right-handed orientation, depending on the golfer tobe tested. The selection of the left-handed orientation requires one setof coordinates are used for the left-handed golfer and right-handedsystem requires another set of coordinates for a right-handed golfer. Atthis time, the system is also set up as either a test or ademonstration. If the test mode is selected, the system will save thetest data, while in the demonstration mode it will not save the data.

At step S103, additional data specific to the location of the test andthe golfer is entered as well. Specifically, the operator enters datafor ambient conditions such as temperature, humidity, wind speed anddirection, elevation, and type of turf to be used in making thecalculations for the golf ball flight, roll, and total distance. Theoperator also inputs the personal data of the golfer. This personal dataincludes name, age, handicap, gender, golf ball type (for use intrajectory calculations discussed below), and golf club used (type, clubhead, shaft).

After this data is entered, the system is ready for use and moves tostep S104. At step S104, the system waits for a sound trigger from themicrophone. When there is a sound of a sufficient level or type, thesystem takes two images (as shown in FIG. 4) of the golf ball in thepredetermined field-of-view separated by a short time interval,preferably 800 microseconds, with each of the two cameras 136, 138 (asshown in FIG. 6). The images recorded by the silicon panel 39 are usedby the system to determine the flight characteristics of the golf ball.

At steps S105-S107, the system uses several algorithms stored in thecomputer to determine the location of the golf ball relative to themonitor. After the computer has determined the location of the golf ballfrom the images, the system (and computer algorithms) determine thelaunch conditions. These determinations, which correspond to steps S105,S106, and S107, include locating the bright areas in the images,determining which of those bright areas correspond to the dots on thegolf ball, and, then using this information to determine the location ofthe golf ball from the images, and calculate the launch conditions,respectively. Specifically, the system, at step S105, analyzes theimages recorded by the cameras by locating the bright areas in theimages. A bright area in the image corresponds to light from the flashbulb assembly 144 reflecting off of the retro-reflective dots or markerson the golf ball. Since the golf ball preferably has 6 dots on it, thesystem should find twelve bright areas that represent the dots in theimages from each of the cameras (2 images of the golf ball with 6 dots).The system then determines which of those bright areas correspond to thegolf ball's reflective dots at step S106. As discussed in detail belowwith reference to FIG. 20, this can be done in several ways. If onlytwelve dots are found in the image, the system moves on to step S107 todetermine, from the dots in the images, the position and orientation ofthe golf ball during the first and second images. However, if there aremore or less than twelve dots or bright areas found in the images, thenat step S108 the system allows the operator to manually change theimages. If too few bright areas are located, the operator adjusts theimage brightness, and if too many are present, the operator may deleteany additional bright areas. In some instances, the bright areas in theimages may be reflections off of other parts of the golf ball or off thegolf club head. If it is not possible to adequately adjust thebrightness or eliminate those extraneous bright areas, then the systemreturns the operator to step S104 to have the golfer hit another golfball. If the manual editing of the areas is successful, however, thenthe system goes to step S107.

At step S107, the system uses the identification of the dots in stepS106 to determine the location of the centers of each of the twelve dotsin each of the two images. Knowing the location of the center of each ofthe dots, the system can calculate the golf ball's spin rate, velocity,and direction.

At step S109, the system uses this information, as well as the ambientconditions and the golf ball information entered at step S103 tocalculate the trajectory of the golf ball during the shot. The systemwill also estimate where the golf ball will land (carry), and even howfar it will roll, giving a total distance for the shot. Because thesystem is calibrated in three dimensions, the system will also be ableto calculate if the golf ball has been sliced or hooked, and how far offline the ball will be.

This information (i.e., the golfer's launch conditions) is thenpresented to the golfer at step S110, in numerical and/or graphicalformats. At step S111, the system can also calculate the sameinformation if a different golf ball had been used (e.g., a two-piecerather than a three-piece golf ball). It is also possible to determinewhat effect a variation in any of the launch conditions (golf ballspeed, spin rate, and launch angle) would have on the results.

The golfer also has the option after step S112 to take more shots byreturning the system to step S104. If the player had chosen the testmode at step S103 and several different shots were taken, at step S113the system calculates and presents the average of all data accumulatedduring the test. At step S114, the system presents the golfer with theideal launch conditions for the player's specific capabilities, therebyallowing the player to make changes and maximize distance. The systemallows the golfer to start a new test with a new golf club, for example,at step S116, or to end the session at S116.

Now turning to the first of these steps in detail (FIG. 19), thecalibration of the system begins with setting up and leveling the systemin step S120. The system is preferably set up on level ground, such as apractice tee or on a level, large field. Obviously, it is also possibleto perform the tests indoors, hitting into a net. Referring to FIGS.6-8, to level the system, the operator uses the threaded rods 128, 130and nuts 132, 134. Referring to FIGS. 7 and 8, the system is positionedto set the best view of the event and the predetermined field-of-view.Then at step S121, the calibration fixture 170 is placed in theappropriate location, which is at the end of the distance calibrators158, 160. The calibration fixture 170 must be level and parallel to thesystem to ensure the best reflection of the light from the flash bulbassembly 144. Placing the calibration fixture at the end of the distancecalibrators 158, 160 ensures that during the test, the calibrationfixture 170 and the golf ball are in full view of each of the cameras.Both cameras take a picture of the calibration fixture and send theimage to a buffer in step S122.

In step S123, the system, including a calibration algorithm, must thendetermine the location of the centers of the spots in each imagecorresponding to the calibration fixture's retro-reflective dots. In oneembodiment, the system locates the centers of these spots by identifyingthe positions of the pixels in the buffer that have a light intensitygreater than a predetermined threshold value. Since the images aretwo-dimensional, the positions of the pixels have two components (x,y).The system searches the images for bright areas and finds the edges ofeach of the bright areas. The system then provides a rough estimate ofthe centers of each of the bright areas. Then all of the bright pixelsin each of the bright areas are averaged and an accurate dot positionand size are calculated for all 15 areas. Those with areas smaller thana minimum area are ignored.

Once the location of each of the dots on the calibration fixture withrespect to camera are determined, the system must know the true spacingof the dots on the calibration fixture. As shown in FIG. 15, thecalibration fixture has dots arranged in three rows and five columns.The dots are placed about one inch apart, and on three separate X planesthat are 1.5 inches apart. The X, Y, and Z coordinates of the center ofeach dot 170 a-o, which are arranged in a three-dimensional pattern,were pre-measured to accuracy of one of one-ten thousandth of an inch ona digitizing table and stored in the computer. The system recalls thepreviously stored data of the three-dimensional positions of the dots onthe calibration fixture relative to one another. The recalled datadepends on the whether a right-handed (X-axis points toward the golfer)or a left-handed (X-axis points away from the golfer) system is used.Both sets of data are stored and can be selected by the operator at stepS124. An exemplary set of these three dimensional positions for righthand calibration for the calibration fixture with 15 dots appear below:

(1) −1.5 3.0 0.0 (2) 1.5 3.0 1.0 (3) 0.0 3.0 2.0 (4) 1.5 3.0 3.0 (5)−1.5 3.0 4.0 (6) −1.5 2.0 0.0 (7) 1.5 2.0 1.0 (8) 0.0 2.0 2.0 (9) 1.52.0 3.0 (10) −1.5 2.0 4.0 (11) −1.5 1.0 0.0 (12) 1.5 1.0 1.0 (13) 0.01.0 2.0 (14) 1.5 1.0 3.0 (15) −1.5 1.0 4.0

An exemplary set of these three dimensional positions for left handcalibration for the calibration fixture with 15 dots appear below:

(1) 1.5 3.0 4.0 (2) −1.5 3.0 3.0 (3) 0.0 3.0 2.0 (4) −1.5 3.0 1.0 (5)1.5 3.0 0.0 (6) 1.5 2.0 4.0 (7) −1.5 2.0 3.0 (8) 0.0 2.0 2.0 (9) −1.52.0 1.0 (10) 1.5 2.0 0.0 (11) 1.5 1.0 4.0 (12) −1.5 1.0 3.0 (13) 0.0 1.02.0 (14) −1.5 1.0 1.0 (15) 1.5 1.0 0.0

At step S125, using the images of the calibration fixture, the systemdetermines eleven (11) constants relating image space coordinates U andV to the known fifteen X, Y, and Z positions on the calibration fixture.The equations relating the calibrated X(I), Y(I), Z(I) spaced pointswith the U_(i) ^(j), V_(i) ^(j) image points are: $\begin{matrix}{U_{i}^{j} = \frac{{D_{1j}{X(i)}} + {D_{2j}{Y(i)}} + {D_{3j}{Z(i)}} + D_{4j}}{{D_{9j}{X(i)}} + {D_{10j}{Y(i)}} + {D_{11j}{Z(i)}} + 1}} & \left( {{Eq}.\quad 1} \right)\end{matrix}$

where i=1, 15; j=1,2. $\begin{matrix}{V_{i}^{j} = \frac{{D_{5j}{X(i)}} + {D_{6j}{Y(i)}} + {D_{7j}{Z(i)}} + D_{8j}}{{D_{9j}{X(i)}} + {D_{10j}{Y(i)}} + {D_{11j}{Z(i)}} + 1}} & \left( {{Eq}.\quad 2} \right)\end{matrix}$

The eleven constants, D_(i1)(I=1,11), for camera 136 and the elevenconstants, D_(i2) (I=1,11), for camera 138 are solved from knowing X(I),Y(I), Z(I) at the 15 locations and the 15 U_(i) ^(j), V_(i) ^(j)coordinates measured in the calibration photo for the two cameras.

In another embodiment, during image analysis the system uses thestandard Run Length Encoding (RLE) technique to locate the bright areas.The RLE technique is conventional and known by those of ordinary skillin the art. Image analysis can occur during calibration or during anactual shot. Once the bright areas are located using the RLE technique,the system then calculates an aspect ratio of all bright areas in theimage to determine which of the areas are the retro-reflective markers.The technique for determining which bright areas are the dots isdiscussed in detail below with respect to FIG. 20.

As noted above, once the system is calibrated in step S102, the operatorcan enter the ambient conditions, including temperature, humidity, wind,elevation, and turf conditions. Next, the operator inputs data about thegolfer. For example, the operator enters information about the golfer,including the golfer's name, the test location, gender, age and thegolfer's handicap. The operator also identifies the golf ball type andclub type, including shaft information, for each test.

A golf ball is then set on a tee where the calibration fixture waslocated and the golfer takes a swing. The system is triggered when asound trigger from the club hitting the golf ball is sent via microphoneto the system. The strobe light unit is activated causing a first imageto be recorded by both cameras. There is an intervening, predeterminedtime delay, preferably 800 microseconds, before the strobe light flashesagain. The time delay is limited on one side by the ability to flash thestrobe light and on the other side by the field-of-view. If the timedelay is too long, the field-of-view may not be large enough to capturethe golf ball in the cameras' views for both images. The cameras used inthe systems 10 and 100 allow for both images (which occur during thefirst and the second strobe flashes) to be recorded in one image frame.Because the images are recorded when the strobe light flashes (due toreflections from the retro-reflective material on the golf ball), theflashes can be as close together as needed without concerns for theconstraints of a mechanically shuttered camera.

This sequence produces an image of the reflections of light off of theretro-reflective dots on each light sensitive panel of the cameras. Thelocation of the dots in each of the images are preferably determinedwith the RLE technique which was discussed for the calibration fixture.

The technique used for determining the aspect ratio to determine whichbright areas are dots will now be described in conjunction with FIG. 20.As shown in step S130, the image must have an appropriate brightnessthreshold level chosen. By setting the correct threshold level for theimage to a predetermined level, all pixels in the image are shown eitheras black or white. Second, at step S131, the images are segmented intodistinct segments, corresponding to the bright areas in each of theimages. The system, at step S132, determines the center of each area byfirst calculating the following summations at each of the segments usingthe following equations:

S _(x) =ΣX _(i)  (Eq. 3)

 S _(y) =ΣY _(i)  (Eq. 4)

S _(xx) =ΣX _(i) ²  (Eq. 5)

S _(yy) =ΣY _(i) ²  (Eq. 6)

S _(xy) =ΣX _(i) Y _(i)  ((Eq. 7)

Once these sums, which are the sums of the bright areas, have beenaccumulated for each of the segments in the image, the net moments aboutthe x and y axes are calculated using the following equations:$\begin{matrix}{I_{x} = {S_{xx} - \frac{S_{x}^{2}}{AREA}}} & \left( {{Eq}.\quad 8} \right) \\{I_{y} = {S_{yy} - \frac{S_{y}^{2}}{AREA}}} & \left( {{Eq}.\quad 9} \right) \\{I_{xy} = {S_{xy} - \frac{S_{x}S_{y}}{AREA}}} & \left( {{Eq}.\quad 10} \right)\end{matrix}$

where AREA is the number of pixels in each bright area.

At step S133, the system eliminates those areas of brightness in theimage that have an area outside a predetermined range. Thus, areas thatare too large and too small are eliminated. In the preferred embodiment,the dots on the golf ball are ¼″-⅛″ and the camera has 753×244 pixels,so that the dots should have an area of about 105 pixels in the images.However, glare by specular reflection, including that from the club headand other objects, may cause additional bright areas to appear in eachof the images. Thus, if the areas are much less or much more than 105pixels, then the system can ignore the areas since they cannot be amarker on the golf ball.

For those areas that remain (i.e., that are approximately 105 pixels)the system determines which are the correct twelve in the followingmanner. The system assumes that the dots will leave an elliptical shapein the image due to the fact that the dots are round and the golf ball'smovement during the time that the strobe light is on. Therefore, at stepS134 the system then calculates the principal moments of inertia of eacharea using the following equations: $\begin{matrix}{I_{x^{\prime}} = {\frac{I_{x} + I_{y}}{2} + \sqrt{\left( \frac{I_{x} - I_{y}}{2} \right)^{2} + I_{xy}^{2}}}} & \left( {{Eq}.\quad 11} \right) \\{I_{y^{\prime}} = {\frac{I_{x} + I_{y}}{2} - \sqrt{\left( \frac{I_{x} - I_{y}}{2} \right)^{2} + I_{xy}^{2}}}} & \left( {{Eq}.\quad 12} \right)\end{matrix}$

Finally, at step S136 the aspect ratio is calculated using the followingequation: $\begin{matrix}{R = \frac{I_{x^{\prime}}}{I_{y^{\prime}}}} & \left( {{Eq}.\quad 13} \right)\end{matrix}$

and the dot is rejected at step S137 if the aspect ratio is greater thanfour or five.

Returning to FIG. 18, once the locations of the dots are determined, thesystem computes the translational velocity of the center of the golfball and angular velocity (spin rate) of the golf ball at step S107 inthe following manner. First, the system uses the triangulation from thedata of cameras to locate the position of the six dots on the surface ofthe golf ball. Specifically, the system solves the set of four linearequations shown below to determine the position (x,y,z) in the golfball's coordinate system of each dot on the surface of the golf ball.

(D _(9,1) U ¹ −D _(1,1))x+(D _(10,1) U ¹ −D _(2,1))y+(D _(11,1) U ¹ −D_(3,1))z+(U ¹ −D _(4,1))=0  (Eq. 14)

 (D _(9,1) V ¹ −D _(5,1))x+(D _(10,1) V ¹ −D _(6,1))y+(D _(11,1) V ¹ −D_(7,1))z+(V ¹ −D _(8,1))=0  (Eq. 15)

(D _(9,2) U ² −D _(1,2))x+(D _(10,2) U ² −D _(2,2))y+(D _(11,2) U ² −D_(3,2))z+(U ² −D _(4,2))=0  (Eq.16)

(D _(9,2) V ² −D _(5,2))x+(D _(10,2) V ² −D _(6,2))y+(D _(11,2) V ² −D_(7,2))z+(V ² −D _(8,2))=0  (Eq. 17)

where D_(ij) are the eleven constants determined by the calibrationmethod at steps S102 (FIG. 18) and S125 (FIG. 19), where i identifiesthe constant and j identifies the image.

Next, the system converts the dot locations (determined at step S135,FIG. 20) in the golf ball coordinate system to the reference globalsystem of the calibrated cameras 136, 138 using the following matrixequation: $\begin{matrix}{\left\lfloor \begin{matrix}x_{g} \\y_{g} \\z_{g}\end{matrix} \right\rfloor = {\left\lfloor \begin{matrix}T_{x} \\T_{y} \\T_{z}\end{matrix} \right\rfloor + {\left\lfloor \begin{matrix}M_{11} & M_{12} & M_{13} \\M_{21} & M_{22} & M_{23} \\M_{31} & M_{32} & M_{33}\end{matrix} \right\rfloor \quad \left\lfloor \begin{matrix}x_{b} \\y_{b} \\z_{b}\end{matrix} \right\rfloor}}} & \left( {{Eq}.\quad 18} \right)\end{matrix}$

where Xg, Yg, Zg are the global coordinates of the center of the golfball. The column vector, T_(x),T_(y),T_(z), is the location of thecenter of the golf ball in the global coordinate system. The matrixelements M_(ij)(i=1,3; j=1,3) are the direction cosines defining theorientation of the golf ball coordinate system relative to the globalsystem. The three angles a₁,a₂,a₃ describe the elements of matrix M_(ij)in terms of periodic functions. Substituting matrix equation for theglobal position of each reflector into the set of four linear equationsshown above, a set of 28 equations result for the six unknown variables(T_(x),T_(y),T_(z),a₁,a₂,a₃). A similar set of 28 equations must besolved for the second image of the golf ball. Typically, the solution ofthe three variables T_(x),T_(y),T_(z) and the three angles at a₁,a₂,a₃that prescribed the rotation matrix M is solvable in four iterations forthe 28 equations that must be simultaneously satisfied.

The kinematic variables, three components of translational velocity andthree components of angular velocity in the global coordinate system,are calculated from the relative translation of the center of mass andrelative rotation angles that the golf ball makes between its two imagepositions.

The velocity components of the center of mass V_(x),V_(y),V_(z) alongthe three axes of the global coordinate system are given by thefollowing equations:${V_{x} = \frac{{T_{x}\left( {t + {\Delta \quad T}} \right)} - {T_{x}(t)}}{\Delta \quad T}};$${V_{y} = \frac{{T_{y}\left( {t + {\Delta \quad T}} \right)} - {T_{y}(t)}}{\Delta \quad T}};$$V_{z} = \frac{{T_{z}\left( {t + {\Delta \quad T}} \right)} - {T_{z}(t)}}{\Delta \quad T}$

(Eqs. 19, 20, and 21, respectively) in which t is the time of the firststrobe measurement of T_(x),T_(y),T_(z) and ΔT is the time betweenimages.

The spin rate components in the global axis system result from obtainingthe product of the inverse orientation matrix, M^(T)(t) and M(t+ΔT). Theresulting relative orientation matrix, A, A(t,t+Δt)=M(t+Δt)M^(T)(t),measures the angular difference of the two strobe golf ball images.

The magnitude Θ of the angle of rotation about the spin axis during thetime increment ΔT is given by: $\begin{matrix}{\theta = {\sin^{- 1}\left( \frac{R}{2} \right)}} & \left( {{Eq}.\quad 22} \right)\end{matrix}$

where

R={square root over (1²+m²+n²)};

l=A₃₂−A₂₃; m=A₁₃−A₃₁; and n=A₂₁−A₁₂.

The three orthogonal components of spin rate, W_(x),W_(y),W_(z), aregiven by the following equations: $\begin{matrix}{W_{x} = \frac{\Theta \quad L}{R\quad \Delta \quad t}} & \left( {{Eq}.\quad 23} \right) \\{W_{y} = \frac{\Theta \quad M}{R\quad \Delta \quad t}} & \left( {{Eq}.\quad 24} \right) \\{W_{z} = \frac{\Theta \quad N}{R\quad \Delta \quad t}} & \left( {{Eq}.\quad 25} \right)\end{matrix}$

At step S109 of FIG. 18, the system, including a computer algorithm,then computes the trajectories for the tests using the initial velocityand initial spin rate which were computed in step S107. For each timeincrement, the system interpolates the forces on the golf ball at time Tand calculates the velocity at time T+1 from the velocity of the golfball and the forces on the golf ball at time T. Next, the systemcomputes the mean velocity and the Reynold's number, which is the ratioof the flow's inertial forces to the flow's viscous forces during thetime interval from time T to time T+1. The system then interpolates themean forces, from which the system calculates the velocity at time T+1.The forces include the drag force, the lift due to the spin of the golfball, and gravitational forces. Using the velocity at time T+1, thesystem can compute the position at time T+1. Finally, the systemcomputes the spin rate at time T+1. In the preferred embodiment, thelength of the time interval is 0.1 seconds. This calculation isperformed until the golf ball reaches the ground.

The system uses the following equations to perform these calculations.For the drag force on the golf ball, the force is calculated by:

F _(d) =c _(d)*½*ρ*|V ^(Bf)|² *A;  (Eq. 26)

where

c_(d)=drag coefficient previously determined and stored in a data filethat is called when the golf ball type is selected;

ρ=density of air—entered at step S103, the beginning of the test;

|V^(Bf)|=magnitude of the velocity of the golf ball; and

A=the cross-sectional area of the golf ball—also known from the golfball selected.

The lift, caused by the spin of the golf ball, is perpendicular to thevelocity direction and spin direction and is given by:

n _(L) =N _(ω) ×n _(VB),  (Eq. 27)

where n _(L), N _(ω), and n _(VB) are the direction cosines of the liftforce, the angular rotation of the golf ball, and the velocity of thegolf ball, respectively.

The magnitude of the lift is given by:

F _(L) =c _(L)*½*ρ*|V ^(Bf)|² *A  (Eq. 28)

where c_(L) is the lift coefficient and the other terms being definedabove.

Therefore, the applied aerodynamic force on the golf ball becomes

R ^(B) =n _(L) F _(L) −n _(VB) F _(d)  (Eq. 29)

The velocity and spin of the golf ball are then transformed into the X,Y, and Z directions so that generalized velocities and rotationalvelocities are given by

  V ^(Bf) =u ₉ X+ u ₁₀ Y+ u ₁₁ Z   (Eq. 30)

ω ^(Bf) =u ₁₂ X+ u ₁₃ Y+ u ₁₄ Z   (Eq. 31)

where u₉, u₁₀, and u₁₁, are the velocities in the X, Y, and Zdirections; and u₁₂, u₁₃, and u₁₄ are the spin velocities in the X, Y,and Z directions.

Using these equations, the system obtains the following second orderdifferential equations:

n _(1x) *F ₁ −n _(Vbx) *F _(d) −m _(B) *u ₉=0  (Eq. 32)

n _(1y) *F ₁ −n _(Vby) *F _(d) −m _(B) *u ₁₀=0  (Eq. 33)

n _(1z) *F ₁ −n _(Vbz) *F _(d) −m _(B) *u ₁₁−m_(B)*g=0  (Eq. 34)

where

n_(1x), n_(1y), n_(1z) are the direction cosines of the force in the X,Y, and Z directions, respectively;

n_(Vbx), n_(Vby), and n_(Vbz) are the directions of the velocity vectorsin the X, Y, and Z directions, respectively;

m_(B) is the mass of the ball; and

m_(B)*g relates to the gravitational force exerted on the golf ball inthe Z direction.

These second order differential equations are then solved for each timestep, preferably every 0.1 second using the drag and lift coefficients(C_(d) and C_(L)) from data files, or from another source, based uponthe velocity (V ^(Bf)) and angular velocity (ω^(Bf)) at each of thosetime steps.

The trajectory method repeats this procedure for successive timeintervals until the computed elevation component of the golf ball'sposition is less than a predetermined elevation, usually zero or groundlevel. See FIG. 21. When the golf ball reaches ground level, the methodinterpolates to compute the ground impact conditions including finalvelocity, trajectory time, impact angle, and spin rate. Using a rollmodel based on empirical data and golf ball data input by the operator,the system computes the final resting position of the golf ball usingthe just-computed ground impact conditions. Accordingly, the systemcomputes the total distance from the tee to the final resting positionof the golf ball. A data file stores the results computed by thetrajectory method.

The system then determines whether an additional test will be performed.If additional tests are to be performed, the process described aboverepeats, beginning at step S104 with the sound trigger through step S110where the trajectory method computes and presents the trajectory for thegolf ball.

When all tests have been performed, the analysis method computesstatistics for each golf ball type used in the tests and presents theresults to the operator. For the group of tests performed for each golfball type, the system computes the average value and standard deviationfrom the mean for several launch characteristics including the velocity,the launch angle, the side angles, the backspin, the side spin, and thecarry and roll.

Different factors contribute to the standard deviation of themeasurements including the variation in the compression and resilienceof the golf balls, the variation in the positioning of the dots on thegolf balls, the pixel resolution of the light sensitive panels and theaccuracy of the pre-measured dots on the calibration fixture. Obviously,the primary source of scatter lies in the swing variations of thetypical golfer.

Upon request from the operator, the system will display the test resultsin various forms. For example, the system will display individualresults for the golf ball type selected by the operator.

Similarly, the system in step S113 can also display tabularrepresentations of the trajectories for the golf ball types selected bythe operator. The tabular representation presents trajectory informationincluding distance, height, velocity, spin, lift, drag, and theReynold's number. Similarly, the analysis method displays graphicalrepresentation of the trajectories for the golf ball types selected bythe operator. The system computes the graphical trajectories from theaverage launch conditions computed for each golf ball type.

At step S113, the system displays the average of each of the shots takenby the golfer. The results are displayed in a tabular and/or graphicalformat. The displayed results include the total distance, the spin rate,the launch angle, distance in the air, and golf ball speed. From thisinformation, the system at step S114 shows the golfer the results if thelaunch angle and spin rate of the golf ball were slightly changed,allowing the golfer to optimize the equipment and/or swing. As shown inFIG. 22, the distance the golf ball travels is dependent on the initialspin rate and launch angle for a given golf ball speed. It is assumedthat the golfer will not be able to increase the golf ball speed, whichin turn is determined by the club head speed. (One way to increase thegolf ball and club head speed, is to increase the shaft length. However,increasing the shaft length may change other variables, including thelaunch angle and spin rate, so a new set of tests should be done.)

At step S114, the system calculates the distances of a golf ball struckat a variety of launch angles and spin rates that are close to those forthe golfer. The operator is able to choose which launch angles and spinrates are used to calculate the distances. One example is shown in FIG.22. In this example, the system calculated the distances that a golfball having an initial velocity of 130 mph will travel for launch anglesof 0° to 15° and having initial spin rates from 2000 rpm to 4000 rpm. Inorder to display this particular data, the system performs thetrajectory calculations described above between about 50-100 times(several predetermined values of launch angles and several predeterminedvalues of initial spin rates). The operator can dictate the range oflaunch angles and spin rates the system should use, as well as how manyvalues of each the system uses in the calculations. From the graphicaldata in FIG. 22, the golfer can determine which of these two variablescould be changed to improve the distance.

Using FIG. 22, if the golfer had a launch angle of L₂ degrees and a spinrate of S₂ rpm, the golfer would attain a distance within the range of220 to 225 yards. If the golfer reduced the spin rate from S₂ rpm to S₁rpm, the distance attained would increase to the range of 225 to 230yards. Similarly at a spin rate of S₁ a change in the launch angle fromL₁ degrees to L₂ degrees would also increase the distance. The spin rateand launch angle can be altered simultaneously to change the distances.Knowing this information, the golfer can make the appropriateadjustments to achieve this increase in distance.

Since the golfer's data is saved, when the system is in the test mode,it is also possible to compare the golfer's data with that of othergolfers, whose data were also saved. In this way, it is possible forgolfers to have their data (launch angle, initial golf ball speed, spinrate, etc.) compared to others. This comparison may be done in a tabularor graphical format. Similarly, the system may compare the data fromsuccessive clubs (e.g., a 5-iron to a 6-iron to a 7-iron) to determineif there are gaps in the clubs (inconsistent distances between each ofthe clubs). Alternatively, two different golfers could be compared usingthe same or different clubs, or the same or different balls.

EXAMPLE

After calibration, a golf machine struck six balata wound golf balls andsix two-piece solid golf balls under the same conditions. The followingdata for golf ball movement was obtained:

Launch W_(x) W_(y) W_(z) Ball Speed Angle Side Angle Rate Rate RateUnits mph degrees degrees rpm rpm rpm Average 156.7 8.5 −0.7 −4403 3 193(Wound) Standard 0.8 0.4 0.2 184 78 115 Deviation Average 156.6 8.8 −0.7−3202 3 −23 (Two-Piece) Standard 1.0 0.3 0.2 126 197 137 Deviation

These results illustrate the effect of two different golf ballconstructions on launch conditions. The launch variable primarilyaffected is the resulting backspin of the golf ball (W_(x) rate) onsquarely hit golf shots. A secondary effect is the lower launch angle ofwound construction versus two-piece solid golf balls with high modulusionomer cover material.

While the above invention has been described with reference to certainpreferred embodiments, it should be kept in mind that the scope of thepresent invention is not limited to these embodiments. One skilled inthe art may find variations of these preferred embodiments which,nevertheless, fall within the spirit of the present invention, whosescope is defined by the claims set forth below.

What is claimed is:
 1. A method of reducing extraneous areas ofbrightness in an image of a spinning sphere having contrasting elements,comprising the steps of: segmenting the image into a respective numberof areas of brightness; calculating the center of each of the areas ofbrightness; determining the principle axes of the areas of brightness;calculating a ratio of the principle axes of each area of brightness;eliminating the area of brightness if the ratio of the principle axesexceeds a predetermined value.
 2. The method of claim 1, wherein thestep of calculating the center of each of the areas of brightnessincludes performing a plurality of summations for the areas ofbrightness and calculating net moments about two axes.
 3. The method ofclaim 1, wherein the segmenting step is preceded by setting a brightnessthreshold level in the image to a predetermined level.
 4. The method ofclaim 1, wherein the center calculating step is preceded by eliminatingareas of brightness in the image that have an area different from apredetermined area.
 5. The method of claim 4, wherein the predeterminedarea is about 105 pixels.
 6. A method of filtering an image of a movingobject having reflective markers comprising the steps of: displayingportions of the image which have a brightness above a predeterminedthreshold level in a first color; displaying portions of the image whichhave a brightness below the threshold level in a second color;segmenting the first color portions into areas of brightness;eliminating areas of brightness in the image that have an area outside apredetermined range; and eliminating areas of brightness in the imagethat have an aspect ratio greater than a predetermined value.
 7. Themethod of claim 6, wherein the predetermined value is
 4. 8. The methodof claim 6, wherein the predetermined value is
 5. 9. A method ofprocessing images of a moving object having reflective markerscomprising the steps of: capturing at least one bright image of theobject; dividing the image into a plurality of pixels; assigning a colorto each pixel, the assigned color being either a first color if thepixel has a brightness above a predetermined threshold level or anothercolor if the pixel has a brightness below the predetermined thresholdlevel; connecting adjacent pixels of the first color to form brightareas; corresponding the bright areas to the markers on the object; andcalculating the location of the markers from the at least one image. 10.The method of claim 9, wherein the capturing step further comprises thesteps of: capturing a first pair of images on a first image frame of afirst camera; and capturing a second pair of images on a second imageframe of a second camera.
 11. The method of claim 9, wherein thecalculating step further comprises the step of mathematically comparingthe first pair of images with the second pair of images.
 12. The methodof claim 9, wherein the corresponding step further comprises the step ofeliminating extraneous areas of brightness from the image.
 13. Themethod of claim 9, further comprising determining at least one of thetransverse velocity and spin rate of the object.
 14. The method of claim9, wherein the dividing includes dividing the image into rows andcolumns of pixels.
 15. The method of claim 14, wherein the dividingfurther includes dividing the image into 753 pixels by 244 pixels. 16.The method of claim 9, further comprising: determining if any of thebright areas are aberrant bright areas that do not correspond to one ofthe markers; and ignoring the aberrant bright areas.
 17. The method ofclaim 16, wherein the determining includes determining whether any ofthe bright areas have an area outside a predetermined range of areas.